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[/] [astron_requantizer/] [trunk/] [common_requantize.vhd] - Blame information for rev 4

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-------------------------------------------------------------------------------
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--
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-- Copyright 2020
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-- ASTRON (Netherlands Institute for Radio Astronomy) <http://www.astron.nl/>
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-- P.O.Box 2, 7990 AA Dwingeloo, The Netherlands
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-- 
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-- Licensed under the Apache License, Version 2.0 (the "License");
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-- you may not use this file except in compliance with the License.
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-- You may obtain a copy of the License at
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-- 
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--     http://www.apache.org/licenses/LICENSE-2.0
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-- 
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-- Unless required by applicable law or agreed to in writing, software
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-- distributed under the License is distributed on an "AS IS" BASIS,
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-- WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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-- See the License for the specific language governing permissions and
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-- limitations under the License.
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--
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-------------------------------------------------------------------------------
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LIBRARY IEEE, common_pkg_lib;
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USE IEEE.std_logic_1164.ALL;
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USE IEEE.numeric_std.ALL;
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USE common_pkg_lib.common_pkg.ALL;
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-- Purpose: Requantize the input data to the output data width by removing
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--          LSbits and/or MSbits
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-- Description:
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--
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-- . in_dat --> remove LSbits --> rem_dat --> remove MSbits --> shift left by c_gain_w --> out_dat
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--
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-- . Remove LSBits by means of ROUND or TRUNCATE
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-- . Remove LSBits when c_lsb_w>0
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--
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-- . Remove MSBits by means of CLIP or WRAP
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-- . Remove MSbits when g_in_dat_w-c_lsb_w > g_out_dat_w:
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--     in_dat   <---------------------g_in_dat_w--------------------->
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--     rem_dat  <---------------------c_rem_dat_w-------><--c_lsb_w-->
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--     res_dat          <-------------g_out_dat_w-------><--c_lsb_w-->
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--
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-- . Extend MSbits when g_in_dat_w-c_lsb_w <= g_out_dat_w::
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--     in_dat           <-------------g_in_dat_w--------------------->
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--     rem_dat          <-------------c_rem_dat_w-------><--c_lsb_w-->
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--     res_dat  <---------------------g_out_dat_w-------><--c_lsb_w-->
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--
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-- . Shift left res_dat before resizing to out_dat'LENGTH, which is useful to keep the res_dat in the MSbits when out_dat'LENGTH > g_out_dat_w
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--     gain_dat <-------g_out_dat_w-------><--c_gain_w-->
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--  
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-- Remarks:
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-- . It is not necessary to define g_msb_w, because the number of MSbits that
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--   need to be removed (or extended) follows from the other widths.
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ENTITY common_requantize IS
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  GENERIC (
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    g_representation      : STRING  := "SIGNED";  -- SIGNED (round +-0.5 away from zero to +- infinity) or UNSIGNED rounding (round 0.5 up to + inifinity)
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    g_lsb_w               : INTEGER := 4;         -- when > 0, number of LSbits to remove from in_dat
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                                                  -- when < 0, number of LSBits to insert as a gain before resize to out_dat'LENGTH
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                                                  -- when 0 then no effect
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    g_lsb_round           : BOOLEAN := TRUE;      -- when true ROUND else TRUNCATE the input LSbits
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    g_lsb_round_clip      : BOOLEAN := FALSE;     -- when true round clip to +max to avoid wrapping to output -min (signed) or 0 (unsigned) due to rounding
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    g_msb_clip            : BOOLEAN := TRUE;      -- when true CLIP else WRAP the input MSbits
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    g_msb_clip_symmetric  : BOOLEAN := FALSE;     -- when TRUE clip signed symmetric to +c_smax and -c_smax, else to +c_smax and c_smin_symm
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                                                  -- for wrapping when g_msb_clip=FALSE the g_msb_clip_symmetric is ignored, so signed wrapping is done asymmetric
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    g_gain_w              : NATURAL := 0;         -- do not use, must be 0, use negative g_lsb_w instead
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    g_pipeline_remove_lsb : NATURAL := 0;         -- >= 0
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    g_pipeline_remove_msb : NATURAL := 0;         -- >= 0, use g_pipeline_remove_lsb=0 and g_pipeline_remove_msb=0 for combinatorial output
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    g_in_dat_w            : NATURAL := 36;        -- input data width
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    g_out_dat_w           : NATURAL := 18         -- output data width
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  );
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  PORT (
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    clk        : IN  STD_LOGIC;
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    clken      : IN  STD_LOGIC := '1';
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    in_dat     : IN  STD_LOGIC_VECTOR;  -- unconstrained slv to also support widths other than g_in_dat_w by only using [g_in_dat_w-1:0] from the in_dat slv
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    out_dat    : OUT STD_LOGIC_VECTOR;  -- unconstrained slv to also support widths other then g_out_dat_w by resizing the result [g_out_dat_w-1:0] to the out_dat slv
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    out_ovr    : OUT STD_LOGIC          -- out_ovr is '1' when the removal of MSbits causes clipping or wrapping
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  );
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END;
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ARCHITECTURE str OF common_requantize IS
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  -- Use c_lsb_w > 0 to remove LSBits and support c_lsb < 0 to shift in zero value LSbits as a gain
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  CONSTANT c_lsb_w        : NATURAL := sel_a_b(g_lsb_w > 0,  g_lsb_w, 0);
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  CONSTANT c_gain_w       : NATURAL := sel_a_b(g_lsb_w < 0, -g_lsb_w, 0);
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  CONSTANT c_rem_dat_w    : NATURAL := g_in_dat_w-c_lsb_w;
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  SIGNAL rem_dat       : STD_LOGIC_VECTOR(c_rem_dat_w-1 DOWNTO 0);  -- remaining in_dat after removing the c_lsb_w number of LSBits
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  SIGNAL res_dat       : STD_LOGIC_VECTOR(g_out_dat_w-1 DOWNTO 0);  -- resulting out_dat after removing the g_msb_w number of MSBits
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  SIGNAL gain_dat      : STD_LOGIC_VECTOR(g_out_dat_w+c_gain_w-1 DOWNTO 0) := (OTHERS=>'0');  -- fill extra LSBits with '0' instead of extending MSbits
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BEGIN
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  ASSERT g_gain_w=0 REPORT "common_requantize: must use g_gain_w = 0, because gain is now supported via negative g_lsb_w." SEVERITY FAILURE;
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  -- Remove LSBits using ROUND or TRUNCATE
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  u_remove_lsb : ENTITY work.common_round
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  GENERIC MAP (
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    g_representation  => g_representation,
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    g_round           => g_lsb_round,
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    g_round_clip      => g_lsb_round_clip,
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    g_pipeline_input  => 0,
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    g_pipeline_output => g_pipeline_remove_lsb,
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    g_in_dat_w        => g_in_dat_w,
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    g_out_dat_w       => c_rem_dat_w
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  )
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  PORT MAP (
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    clk        => clk,
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    clken      => clken,
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    in_dat     => in_dat(g_in_dat_w-1 DOWNTO 0),
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    out_dat    => rem_dat
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  );
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  -- Remove MSBits using CLIP or WRAP
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  u_remove_msb : ENTITY work.common_resize
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  GENERIC MAP (
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    g_representation  => g_representation,
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    g_pipeline_input  => 0,
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    g_pipeline_output => g_pipeline_remove_msb,
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    g_clip            => g_msb_clip,
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    g_clip_symmetric  => g_msb_clip_symmetric,
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    g_in_dat_w        => c_rem_dat_w,
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    g_out_dat_w       => g_out_dat_w
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  )
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  PORT MAP (
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    clk        => clk,
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    clken      => clken,
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    in_dat     => rem_dat,
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    out_dat    => res_dat,
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    out_ovr    => out_ovr
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  );
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  -- Output gain
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  gain_dat(g_out_dat_w+c_gain_w-1 DOWNTO c_gain_w) <= res_dat;
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  out_dat <= RESIZE_SVEC(gain_dat, out_dat'LENGTH) WHEN g_representation="SIGNED" ELSE RESIZE_UVEC(gain_dat, out_dat'LENGTH);
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END str;

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